Since the Injustice 2 comics haven't all been released yet, it's very likely that this will be revealed in a later issue, and as such this question violates the "Future Works" policy.
– DisturbedNeoNov 29 '17 at 10:24

Oops sorry, I didn't know that. So I re-read Injustice 2 from beginning, and indeed there origin of this Batman is not mentioned yet. Guess I'll just speculate :)
– anta40Nov 29 '17 at 11:38

1

I've been informed that the answer to this question is revealed in #46, which indeed seems to be the case. So I'm reopening it as it no longer falls under the Future Works policy.
– Rand al'Thor♦Mar 6 '18 at 14:58

2 Answers
2

In Injustice 2 #46 it is revealed that this is a certain Jason. The familiar dialogue he has with Damian makes me think that this is indeed Jason Todd. Since he was revived with the Lazarus Pit, this would explain his connection with Ra's. Interesting enough however, he has now a bit white hair like Jason Blood who was killed by Spectre in Injustice Year 3.